Coating lumber to prevent end checking



Nov. 8, 1938. M. GRAY COATING LUMBER TO PREVENT END CHECKING Filed June14, 1937 INVENTOR.

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Patented Nov. 8, 1938 I PATENT OFFICE.

oos'rmo LUMBER r PREVENT END cnncmc MlltonGray, Memphis, Tenn., asslgnorto E. L.

Bruce tionof Delaware Application June 14, 1937, Serial No. 148,152

Company, Memphis, Tenn, a corpora- My invention relates to the treatmentof lumber to prevent what is known as end-checking". This object isattained by coating or sealing the transverse end of the lumber with asuitable composition, preferably an asphaltic plastic composition.Lumberm'en have sought for a long time, for a suitable and efi'ectivematerial that would stop end-checking. This is because end checksdevelop into longitudinal splits and in 10 handling, a split tends tobecome longer and eventually depreciates the value of the piece oflumber. 4

Checking in wood, which means wood that has opened up or cracked. iscaused by a tension stress in the outer fibers when they dry faster andattempt to shrink more than the portion located more nearly in thecenter. If the drying process is sufllciently retarded, these stressesdo not operate to such an extent thatthey will be of sufilcient force toopen up the wood or split it. Accordingly, if a satisfactory way can befound that prevents the rapid loss of moisture from the wood and spreadsit over a longer period of time, the drying out process is more uniformas to different parts of the wood.

Since lumber dries more rapidly through the ends than between the ends,this more rapid dryingincreases the tendency to checking at the ends.If, the ends can be prevented from checking, this cuts down thelongitudinal checks for a space back from the end surface suificientlyto keep such longitudinal checks from developing into end checks. v

The material that I apply to the ends of the lumber in order to preventchecking should be plastic, adhesive, not completely moisture proof.water repellent, have a reasonably high resistance to solar rays so thatit will not soften and run under high atmospheric temperatures and 40not crack or become brittleat low atmospheric temperatures. It shouldalso expand and contract without cracking.

Various types of compositions having these physical characteristics, maybe used for this purpose. but one that-I have found satisfactory afterextensive use is compounded as follows:

I melt together a mixture of three difierent types of Mexican asphalts,99.1% soluble in CS2, and in the following proportions:

Percent 235250 F.\(M. P.) 7 160170 F. (M. P.) 53 130 F. (M. 'P.) 40

55 When so compounded, the base asphalt produced has a melting point of-150 F. and penetration at 'l'l F., 30 c. m., minimum and 50 c. m.maximum.

The final composition contains 51% of the above asphalt mixture, 34% ofxxxx asbestos 5 fibre and 15% of mineral spirits. The product is usuallymade by adding one half of the solvent to the asphalt mixture, thenadding the fibre and after this has been thoroughly mixed, the balanceof the solvent is added. The blend of 10 the different types of asphaltprovide a base having the desired physical properties, especially afterthe solvent has evaporated. The asbestos fibre absorbs the liquefiedasphalt to which the solvent has been added. The asphalt itself ab- 16sorbs and retains a large percentage of the solvent. The fibre absorbsthe liquefied asphaltsolvent mixture, and in this manner it preventsthis mixture from penetrating the fibrous structure'of the wood. Thismixture while sticky and 20 .cementicious, is not liquid. Anotherfunction of.

the fibre is to make the mixture flexible and plastic after the solventhas evaporated; The fibre adds to the stability of the mixture andprevents any sag of the mixture. It also bridges 25 the cracks andpores, thus preventing the asphalt from sinking" into the crevices andpores. It also increases the resistance to the heat of solar rays whichwould otherwise cause the material to run under intense solar heat. 30

This product is not molstureproof, but it is waterproof, and it is onlywaterproof to the extent that it will shed and not absorb during heavyrains, However, under pressure, water will transfer through the plasticlayer. Through 35 this layer escape of moisture will be retarded but notprevented. The solvent makes the mass more workable and also causes theproduct to stick better to the end of the wood.

This composition is plastic when used and can 40 be applied to thetransverse ends of the lumber by a putty knife or similar tool, in alayer'of substantial thickness, running from about h of an inch to a:of. an inch.

The composition is effective to prevent end 45 checking in field or kilndrying of lumber and timber.

Referring to the drawing,

Fig. 1 is a perspective view of the end portion of a piece of lumber,with the layer of coating 50 broken away; and e v Fig. 2 isa section onthe line 2-2 of Fig. 1.

The piece or structural lumber I, has applied over the entire end,across the grain of the wood, the coating 2 which is sumciently plastic,so as so to be 'spreadable and adhere to the wood. The coating 2 whenapplied is from to of an inch thick. After the solvent has evaporated,the

dry coating is not sticky. While it has a certain amount of rigidity, itnever gets real hard or brittle and is plastic enough so that it can becut with any sharp edge cutting tool.

When dry, the composition has suflicient adherence to the wood and hassufiicient tensile strength, to prevent to a considerable degree, thegrowth of very small cracks into larger ones. This is true where thecheck is in'the ends and is very small. The corresponding force requiredto hold the check together is also small. In this respect, the asbestosfibres which are interlaced in the composition, serve to increase thetensile strength of the composition, when dry.

I claim:

As an article of manufacture, structural lumcutting tool, issubstantially water repellent but.

not completely moistureproof, has a reasonably high resistance to solarrays so that it will not run under high temperatures and not crack orbecome brittle at low temperatures and will expand and contract at suchtemperatures without cracking. I

MILTON GRAY.

